Lubricating oil composition



I certain special alloy bearings.

Patented Au 13, 1940 PATENT OFFICE LUBRIOATING OIL COMPOSITION HermanE. Ries, Jr., Chicago, Ill., assignor' to Sinclair Refining Company, New York, N. Y.,

a corporation of Maine No Drawing. Application September 22, 1937, Serial No. 165,079

'10 Claims. (Cl. 252-57) This invention relates to improvements in compounded lubricating oils. More particularly the improved lubricating oil compositions of this invention consist essentially of a petroleum lubrieating oil having dissolved therein a minor proportion of an alkyl ester of an aromatic stearic acid. Such compounded lubricating compositions are" characterized by an increased film strength and improved lubricating properties. The term petroleum lubricating oil as used herein is intended to refer to an oil of petroleum origin which has a viscosity upwards of '50-'70 seconds at 100.F. Salbolt Universal.

Efiective lubrication depends to a great extent upon the film strength and viscosity of the lubricant and also upon that property of the lubricant usually referred to as oiliness. Another essential characteristic of a satisfactory lubricant is that it must not corrode or otherwise attack the lubricated parts and the other metal surfaces which it may contact. The present day tendency in the operation of machinery in general and "in the automotive industry in particular is toward higher speeds and increased loads, placing an' ever increasing burden upon-previously satisfactory lubricants. The inability of uncompounded petroleum lubricating oils to meet these increasingly more rigorous requirements has become increasingly apparent. A lubricating'oil composition having an increased film strength and an increased oiliness or adhesive capacity, which does not cause corrosion of the metal surfaces with which it comes in contact and which is stable under normal conditions of use and storage, is therefore highly desirable. Numerous attempts have been made with varying degrees of success to produce such a lubricant. The chief difiiculty encountered in the addition of various chemicals to lubricating oils for this purpose has been a tendency to promote instability or to accelerate the corrosion of the metal surfaces with which the. oil comes into contact. Corrosion difficulties have been particularly marked with respect to A further disadvantage experienced in the use of many-of the proposedaddition agents is that the viscosity or pour point of the resulting compounded mixture is adversely affected, thus greatly limiting their utility. a

I have found that by compounding, with a suitable petroleum lubricating oil, a minor'proportion of an alkyl ester of an aromatic stearic acid, a lubricating oil composition having a substantially increased film strength and oiliness? is produced, when comparedtothe oilprior to compounding.

Further, the use of alkyl esters of aromatic stearic acidsto produce the improved lubricating compositions of the present invention eliminates or minimizes the usual disadvantages experienced in the use of blending agents intended to improve the lubricating properties of the composition. In particular, the tendency toward corrosion of the unblended oil is not increased by the addition of these esters and in some cases it is distinctly lessened. The viscosity index is not materially decreased by the addition of such esters, and in many instances it has been. found to improve with such addition. The pour point of the compounded oils of my invention is not raised by reason of the added ester. In fact it has been found that the pour point is often depressed by from 5 to 20 F. Further, the alkyl esters of aromatic stearic acids herein described are sufiiciently soluble in lubricating oils, and sufiiciently stable to permit the compounding of lubricating compositions of improved film strength which are stable under conditions of ordinary handling and in normal use. The sludge forming and polymerization tendencies of the oil component of the composition are not-affected to any marked degree.

As a result of a great number of very precise measurements and observations of the film strength and area indexes of these esters made on a carefully calibrated hydrophil balance, I have. found that these esters possess very favorable film characteristics. In general it has been found that compounds which exhibit such favorable film characteristics have the property of enhancing the film strength of lubricating compositions when compounded with petroleum oils. As pointed out above, however, many such addition agents when compounded with oils introduce such seriousdisadvantages that their usefor this purpose is either greatly restricted or made impossible. Extensive service tests designed to measure and compare the film strength and effectiveness of lubricating compositions, under conditions "comparable to those existing under conditions i may be prepared by condensing oleic acid and benzol in the presence of aluminum chloride. A

detailed method of preparing this particular aromatic stearlc acid is described in U. S. Patent #2,081,075 granted Arnold C. Vobach on an application filed July 6, 1936. In the method of preparation described in this patent, a crude reaction product is recovered by distillation under reduced pressure. As described, two major cuts may be taken ofif during the fractional distillation under a reduced pressure of 4 millimeters of mercury absolute pressure. The second of these two distillate fractions is composed primarily of phenyl stearic acid, while the first fraction contains other organic acids in addition to phenyl stearic acid, such as for example, palmitic acid and stearic acid. The second of these two distillate fractions can be esterified with an alcohol to produce the product to which I refer to herein as an alkyl ester of phenyl stearic acid, or the first and second fractions may be combined and together esterified to produce an ester mixture whose primary constituent is the ester of the phenyl stearic acid. Any conventional method of esteriflcation may be employed. One suitable method consists in treating an aromatic stearic acid such as is contained in the above referred to second fraction, or in the combined first and second fractions, according to the method described in Organic Syntheses, Gilman, Collective volume, pp. 256-260. After completing the treatment with methyl alcohol and sulfuric acid, the carbon tetrachloride layer which contains the desired ester is separated. The C014 is removed at 300 F. with CO2 gas. The resulting ester product may be employed as the compounding agent in the lubricating composition of the present invention. Other aromatic stearic alkyl esters such as for example the methyl and ethyl esters of tolyl and xylyl stearic acids are prepared in a similar manner with methyl or ethyl alcohol by substituting toluene or xylene for benzene in the original condensation reaction. In the esterification step, the use of C014. as a solvent for the formed ester may be eliminated.

As stated above, the second fraction obtained by the distillation of the reaction products resulting from the condensation of oleic acid and benzol according to the method described by -Vobach is primarily phenyl stearic acid. The

methyl phenyl stearate resulting from the subsequent esterification of this fraction with methyl alcohol is also of relatively high purity, although an ester product of higher purity may be obtained by fractionally distilling the ester product under reduced pressure. In referring to an alkyl ester of an aromatic stearic acid herein I refer to the esterified product constituting the major product of the 'esterification of the second distillate fraction of the method of Vobach in the specific case of phenyl stearic acid or more broadly in the case of other aromatic stearic acids to the esterified product of a so-called heart out resulting from the distillation of the crude reaction product of such a condensation reaction. I also intend by this term to refer to a relatively pure ester of the designated class by whatever process it may be prepared.

It has also been found that the esterified product resulting from the combined first and second distillate fractions of the oleic acid-benzol condensation described in the 'Vobach patent, possesses very favorable film strength and oiliness properties. This mixed ester contains relatively minor proportions of the esters of palmitic and stearic acids. Use of such an ester mixture as the compounding agent in the lubricating 011 compositions of the present invention has the particular advantage that in commercial operation the cost of the compounding agent is considerably reduced. The favorable film strength and oiliness characteristics of the compounded oil have been found to compare favorably with compounded mixtures in which the purer esters have been used as compounding agents. The acid numbers, saponification numbers and iodine numbers of the esterified second fraction and of the esterified combined first and second-fractions as determined in one instance on a condensation of oleic acid and benzol according to the method of Vobach are as follows:

Acid Sapon. Iodine No. No. No.

Methyl ester of second traction 0. 4 145 1.4 Methyl ester 0! combined first and second fractions 0. 267 151 5. 2

In compounding the improved lubricating compositions of the present invention, the allryl ester of an aromatic stearic acid, or the mixed ester containing the alkyl ester of an aromatic stearic acid together with one or both of the alkyl esters of palmitic and stearic acids, is added in minor proportion, and in amount insuflicient materially to alter the normally liquid character of the petroleum lubricating oil itself. For example, when methyl phenyl stearate is the addition agent, it is added to the oil in proportions usually ranging from about 0.5% up to about 2.5% or 3.0% by weight on the oil.

Addition of the described esters in amounts appropriate to produce optimum improvement in the film strength do not materially alter the other important properties of the petroleum oil. Thus, when methyl phenyl stearate is added to a solvent refined, clay treated, residual Pennsylvania aircraft lubricating oil in quantity equivalent to 2.5% by weight on the oil, the addition had the following effect on the compounded mixture. The original oil had an A. P. I. gravity of 28.3, the mixture-27.9. The fiash point remained constant at 510 F. The Saybolt viscosity at F. was reduced from 1498 for the oil to 1364 for the mixture, and at 210 F. from 122.4 for the oil to 115.1 F. for the mixture. The viscosity index was reduced from 107.5 for the oil to 106.8 for the mixture. The pour point was reduced from 15 F. to 10 F, In another example methyl phenyl stearate was added to a Pennsylvania motor oil in the same quantity as above. In this case the addition produced the following results. The A. P. I. gravity was reduced from 28.4 to 28.2; the flash point increased from 425 F. to 435 F.; the viscosity at 100 F. was decreased from 400 to 389, and at 210 F. it was reduced from 59.5 to 58.7; the viscosity index changed from 59.5 to 58.7; the, pour point was lowered from 25 F. to 5 F. In both of the above examples the film strength and oiliness properties of the compounded mixtures were greatly improved when compared to the lubricating oil alone.

I have further found that varying proportions of the free aromatic stearic acid corresponding to the alkyl ester employed, may at times advantageously be present in the addition agent. The quantity of such an acid which is permissibly present, however, is frequently very limited due to the added corrosiveness which may be caused by the presence of the acid.

I claim:

1. The improved lubricating oil composition having increased film strength comprising a petroleum lubricating oil and a minor proportion of an alkyl ester of an aromatic stearic acid.

2. The improved lubricating oil composition having increased film strength comprising a petroleum lubricating oil and a minor proportion of an alkyl ester of phenyl stearic acid.

3. The improved lubricating oil composition having increased film strength comprising a petroleum lubricating oil and a minor proportion of an alkyl ester of tolyl stearic acid.

4. The improved lubricating oil composition having increased film strength comprising a petroleum lubricating oil and a minor proportion of an alkyl ester of xylyl stearic acid.

5. The improved lubricating oil composition having increased film strength comprising a petroleum lubricating oil and a minor proportion.

of the methyl ester oi phenyl stearic acid.

6. The improved lubricating oil composition having increased film strength comprising a petroleum lubricating oil and a proportion of the methyl ester of phenyl stearic acid equivalent to about 2.5% by weight on the oil.

'7. The improved lubricating oil composition having increased film strength comprising apetroleum lubricating oil and minor proportions or an alkyl ester or an aromatic stearic acid.

an alkyl ester of stearic acid and an alkyl ester oi palmitic acid.

8. The improved lubricating oil composition petroleum lubricating oil and a proportion of a mixture of the methyl ester of phenyl stearic having increased film strength comprising a HERMANE. amass. so 

